Accuracy of Field Sobriety Tests

Accuracy of Field Sobriety Tests

Posted By
Jesse Adams

U.S. police officers have been using the three standardized
field sobriety tests (FSTs)–the horizontal gaze nystagmus, the walk-and-turn, and the
one-leg stand—since the late 1970s. The purpose of FSTs is to determine
whether a driver is too intoxicated to drive his or her motor vehicle.
The results are often used as a basis of probable cause for an
OUI arrest.

However, the reliability of these tests is typically questioned. While
police and prosecutors alike depend on FST results for ascertaining a
driver’s level of intoxication, many
criminal defense attorneys believe these tests can sometimes be inaccurate.

How Reliable are Field Sobriety Tests?

To determine the accuracy of FSTs, the NHTSA performed various studies
involving officers. Police officers were tested to see how they could
properly identify a person with a BAC of .1% or higher.

The results of these NHTSA-sponsored tests are the following:

The accuracy rate when all three tests were used together – 82%

The accuracy rate of the horizontal gaze nystagmus – 77%

The accuracy of the walk-and-turn – 68%

The accuracy of the one-leg stand – 65%

When these tests are correct, they only indicate a driver’s BAC level
and not his or her ability to drive a vehicle. Overall, the FSTs are not
a scientifically-proven method to determine intoxication.

There are expert witnesses who study FSTs and understand their vulnerabilities.
Any individual arrested for drunk driving on the basis of a field sobriety
test score is encouraged to challenge their results in an effort to obtain
a favorable outcome in their OUI case.